1. Field of the Invention
This invention relates to steerable conveyances. Certain preferred embodiments are particularly adapted for use in skateboarding.
2. State of the Art
Conveyances that are steerable by leaning or tipping the vehicle body have been available for a number of years. Early embodiments illustrated in U.S. Pat. Nos. 2,44,372 to Bliss; 317,50 to Burton et al.; and 319,839 to Nelson applied the concept of an angled pivot axis to roller skates. As a consequence of the angle of the pivot axis, when the axle rotates with respect to a local coordinate system and about the pivot axis, the axle turns to steer the skates with respect to a global coordinate system. A cogent discussion of the effect of structural arrangements on turning capability of a skateboard is presented in U.S. Pat. No. 4,060,253 to Oldendorf.
In embodiments structured according to the foregoing patent disclosures, a force applied normal to a conveyance platform and along the platform centerline length axis, when the platform is rotated to a maximum turn configuration, fails to cause a return moment effective to urge the conveyance toward a no-turn configuration. That is because the applied force acts directly through the pivot axis, and consequently, has no moment arm. However, a return moment is caused by the compressed rubber suspension components, or spring elements.
Sometimes, it is advantageous for a suspension system to initially resist departure of the axle from a zero-turn configuration that promotes straight-line travel of the conveyance. Such a suspension system may advantageously reduce wobble and thereby promote stability of the conveyance in traveling in an approximately straight line at higher speeds. One such suspension system includes the spring-loaded cam centering arrangement disclosed by Hirt in U.S. Pat. No. 329,556.
An evolution in suspension configurations employing rubber cushion elements is illustrated in combination by U.S. Pat. No. 921,102 to Grout; U.S. Pat. No. 1,550,985 to Schluesselburg; U.S. Pat. No. 3,331,612 to Tietge; and U.S. Pat. No. 4,645,223 to Grossman. An alternative suspension arrangement is illustrated in U.S. Pat. No. 5,263,725 to Gesmer et al., in which is disclosed a suspension configured to avoid damping rubber elements.
In U.S. Pat. No. 1,387,091, Woolley et al. disclose a child's coaster having a support surface arranged to rock along an axle to cause steerable movement of their axle. The load-bearing contact between the axle and support surface is point-contact, and the contact point makes an arcuate path along the support surface. In U.S. Pat. No. 2,330,147, Rodriguez discloses a scooter suspension including a moving pivot axis location, about which axis the scooter body instantaneously rotates. Rodriguez's pivot axis is displaced in a length direction of the axle during a turn. The load-bearing contact at the pivot axis location is disposed between a sliding foot 23 and a support surface of bottom truck 13. Contact between the sliding foot 23 and the support surface of truck 13 during a turn is inherently sliding contact due to the interaction of pin 14 in slot 21, and the radii of foot 23. In U.S. Pat. No. 5,971,411, Jones et al. disclose an axle trapped between parallel walls to permit substantially planar oscillation of the axle relative to the walls. Their axle pivots about a single axis caused by pin 16. The resulting axis of axle rotation is spaced'apart from a contact between the axle 12 and the axle-supporting surface of cushion 13. Therefore, as the axle 12 rotates about the pivot location, the axle inherently scrubs in sliding contact with respect to the axle-supporting surface of cushion 13. A load applied perpendicular to the skateboard deck, at the mid-deck centerline, acts through the pivot axis, and fails to generate a return moment effective to urge the device to a zero-turn configuration.
Each and every one of the aforementioned U.S. patent documents is hereby incorporated into this document in their entirety by this reference for their disclosures of structure related to steerable conveyances. It would be an improvement to provide an axle and suspension system that provides enhanced operational characteristics.